Dendritic cells are a discrete type of white blood cell. Dendritic cells' function is to present antigens to T-lymphocytes. Presentation of antigens to T-lymphocytes results in activation of an immunologic response directed against the antigen. Recent evidence suggests that dendritic cells may be derived from two different precursor cells: myeloid precursor cells or lymphoid precursor cells. Dendritic cells derived from these two precursor sources have identifiable differences, especially in the types of proteins they express on the cell surface. This study is designed to define the panel of genes expressed as dendritic cells developed from the two types of precursor cells. The experiment involves obtaining blood samples from healthy adult volunteers and from umbilical cord blood obtained from placentas following term and pre-term delivery.